Tuning the surface morphology and local atomic structure of Mn-TiO_2 thin films using rapid thermal annealing

摘要

Abstract In this study, Ti~(0.95)Mn~(0.05)O~(2−δ)nanostructured thin films were fabricated by pulsed laser deposition technique followed by rapid thermal annealing (RTA) in pure O~(2)and N~(2)atmospheres. The RTA process induced a substantial change in the surfaces morphology and local atomic structure around Ti_(4+)cation that have been studied by means of atomic force microscopy, Raman scattering and near edge X-ray absorption fine structure (NEXAFS) spectroscopy. Raman spectra of the films were resembled to that of TiO~(2)rutile phase, and the change in the width of E~(g)(434 cm_(−1)) Raman active modes has been attributed to oxygen non-stoichiometry. NEXAFS spectra were carried out in synchrotron facility at Ti/Mn L ~(3,2)edges and O- K edge. The ligand-field splitting, estimated from the energy difference between t~(2g)and e~(g)features in O K-edge spectra were ~ 2.81 eV for pristine and annealed film, which is a characteristic of the TiO~(2)rutile structure, and the asymmetry of t~(2g)and e~(g)bands at the O- K edge has been ascribed to oxygen vacancy (Vo_(2+)). The annealing of film in O~(2)gas optimized the surface structure and healed the Vo_(2+)bridging, while the RTA in N~(2)gas introduced Vo and reduced the valence state of Ti_(4+)(TiO~(2)) into Ti_(3+)(Ti~(2)O~(3)) that have been probed by comparing the NEXAFS spectra of N~(2)annealed film with the reference spectra of Ti~(2)O~(3). Experimental and atomic multiplet calculations revealed that the Mn ions exist in 2+ valence state.